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Author Topic: Open-wire dipoles  (Read 1346 times)
W5LXS
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Posts: 7




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« on: May 03, 2013, 08:36:44 AM »

I have seen a number of articles about building open-wire fed dipoles, usually between 110 and 135 feet in length. I am considering building one as an inverted-vee with the apex at 30 feet and the ends at 8. I understand they are a good choice for 80 thru 10 meters but I haven't seen much on their angle of radiation or if they are good DX antennas. Does anyone know?
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WB6BYU
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Posts: 13020




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« Reply #1 on: May 03, 2013, 09:58:46 AM »

Depends on the band, the angle of the wires, and the desired direction to the DX station.

On 80m and 40m it will act as a low dipole with maximum radiation straight up.  That's not
optimum for DX, which requires a low angle of radiation.

On 20m and higher frequencies the antenna can make some DX contacts, but the slope
of the wires (and the low heights of the ends) reduce the average height:  a shorter
antenna with the same center height may then work better because the average
height is greater.  Also, sloping the wires changes the way that the maximum lobes
from the two sides of the antenna combine, and as the wires get longer (in terms of
wavelengths) on the higher bands it can reach a point where the slope is too much
to launch a signal at useful angles.

So if you want to be able to work the locals on 80m, then the antenna you propose
isn't a bad choice.  But for DX on 20m through 10m, I think you would be better off
with a shorter doublet strung up in the same manner, but with longer ropes so the
ends of the wires are higher up in the air.  The optimum length may be between a
half wave on 40m and one on 20m, depending somewhat on the relative direction to
the DX stations of interest on each band.
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N6GND
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Posts: 333




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« Reply #2 on: May 03, 2013, 10:01:11 AM »

This has been discussed in nearly endless depth in the Antennas and Elmers fora. Do a search with terms like "inverted v," "dipole height" and "open wire feed" and you will find all the information you could possibly hope for. In ten seconds I found the following entry from KE4ZHN posted in 2003. It seems to answer well your primary question.

"The band you operate on also determines the pattern of the antenna. No matter if its a V or flat top, on the higher bands you have many more lobes then on the low bands like 40-80. As a rule, making a dipole an inverted V drops the feedpoint impedance close to 50 ohms, providing a better match to coax, but height also plays a role in this as does the ground under the antenna. Even a flat top dipole isnt great if its only 20 ft off the ground.(this doesnt mean it wont play!) As a rule, higher is better, regardless of band. As you put a flat top up at at least a half wave above the ground, it begins to develope a figure 8 pattern with minor nulls towards the center. But it would be rather tough to get one 125 ft up for 80 mtrs! Most dipoles, regardless of inverted V or flat top have a pretty much omni pattern if less than a half wave off the ground on their respective band. As you go up in frequency, it displays more lobes, some at lower angles on a multiband dipole. This is desirable for dx. The ideal slope angle for an inverted v is around 120 degrees, but its not super critical unless you make it much too sharp, then the efficency takes a dive. In other words, dont make a teepee out of your dipole and expect it to play!"
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N6AJR
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Posts: 9889




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« Reply #3 on: May 03, 2013, 10:39:43 AM »

remember , any antenna is better than no antenna at all.  put it up , try it , and come back and let us know how it worked.
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W5LXS
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Posts: 7




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« Reply #4 on: May 03, 2013, 12:46:15 PM »

Sorry I was unaware of how much attention this topic has gotten. I'm fairly new to the forum so that's my excuse. Thanks for your thoughts.
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N6GND
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Posts: 333




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« Reply #5 on: May 03, 2013, 01:55:17 PM »

Sorry I was unaware of how much attention this topic has gotten. I'm fairly new to the forum so that's my excuse. Thanks for your thoughts.

I wanted to encourage you to delve a bit deeper. Like looking into the advantages/problems of balanced feedines. For instance how balance can be upset by the way the feedline is arranged in relation to the dipole proper; how length of feedline affects the swr at the tuner. And so on.

Best advice is simply to do it. Have fun. Make mistakes. Make improvements. I think trying different antennas is as much fun as anything else in ham radio. Most of us have to work within many physical constraints at our locations. There's a lot of adventure in figuring out the best compromises.
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KB4QAA
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Posts: 2265




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« Reply #6 on: May 03, 2013, 02:37:00 PM »

-A dipole is a dipole, and they should all have the same radiation pattern.

-Ideally, the feed line should not radiate, hence should have no effect on how the antenna operates; Open line, coax, parallel wet string, etc.  Smiley

-Height is the key to better antenna performance.  Having you antenna ends droop to 8ft, is going to cost you much in signal loss due to earth coupling.  Do what you can to get those ends up level.

-Antenna experimenting is one of the most fascinating and cost effective facets of ham radio.  Two books every ham must have:

-ARRL Antenna Book.  Dozens of proven antenna designs with theory from MF-SHF

-ON4UN's Low Band Dxing.  Not just for Dxer's it covers 40m, 80m, 160m.  Easy reading and even more up to date than the ARRL Antenna book.

The web is a vast minefield of half truths, crackpot ideas and often falsehoods about antennas.  Start your research with these two books and you will save much time and confusion!   

Now, get some wire and go play!  bill

bill
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WG8Z
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Posts: 185




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« Reply #7 on: May 03, 2013, 02:45:58 PM »

Put it up and play it.
If you can get the ends up a little higher do so. The flatter you can get it the better.
135' is a good length.
Feedline lengths of mutiples of 50' have worked well for me. (have used 50,100,150)
Balanced tuner works best (johnson matchbox)
also have used icom ah-4 with good results.
I have made  many DX contacts with this antenna.
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K0ZN
Member

Posts: 1531




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« Reply #8 on: May 03, 2013, 04:19:41 PM »

Hi.

That antenna has been my primary antenna for quite a few years; in this case a 130 ft. center fed at 40 ft.  Relative to a wire antenna it works well and I have no
problem at all working DX. You just have to understand that it is not as effective as a 4 element monoband yagi at 90 ft. !! But for what it is, it works very well. You need to understand what happens with harmonic operation, etc. to understand the various patterns or model them. The antenna can and will  have some fairly directional patterns on some bands. On 40 M it is quite directional broadside since it is essentially two half waves in phase;  some gain broadside and a pretty deep null off the ends. On the upper bands the pattern has lobes and nulls. The lobes have a little gain and the nulls can be deep on some bands. It works well on 30 with some directivity in a cloverleaf pattern. On 20 M the nulls don't seem to be too sharp and it works well in most directions except off the ends; I have worked a ton of DX on 20 M with this antenna.
17 M performance is excellent in the directions of the lobes...ditto 15 and 10.  I even use it on 6m where it has a LOT of smaller lobes, but seems to do OK in most directions.  Candidly: I have yet to find a better horizontal all band antenna....actually, all Frequency antenna. On 160 M I tie the ladderline conductors together and feed it as an end fed wire. Works amazingly well and I have had good results with it during the 160 M CW contest; I work coast-to-coast with no problems every year.

There is a reason this antenna has been popular and frequently used since the 1930's: It can work any band, it is a very efficient radiator and mechanical
constructions is simple and cheap. A lot to like. Only down side is that you need a decent antenna tuner. (I use a Johnson KW Matchbox)

FYI:  That antenna will give better performance on the upper HF bands if it is truly horizontal. When you start operating on the higher bands there are a lot of
lobes and in an inverted V configuration, often the resultant radiation pattern is not so good. Usually, harmonic operation is better on a straight horizontal
wire because the patterns stay "clean".  This is not a deal killer. You just have to try it and see; the results become harder to predict. Again, this applies to
the upper bands. on 40 M and down, it is unlikely you would see much difference.

You would find it worth your time to do a little reading in the ARRL Antenna Book and get a better understanding of what is going on with this antenna. It will
help you better understand the differences in radiation pattern by band.

73,  K0ZN
« Last Edit: May 03, 2013, 04:24:30 PM by K0ZN » Logged
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